1. Field of the Invention
This invention relates to food-grade flour and to the production thereof from peanuts. More specifically, this invention relates to the production of a white, defatted, flour by solvent extraction.
2. Description of the Prior Art
There is no known commercial method for the direct solvent extraction of peanuts to produce a peanut flour with all the characteristics of the present invention. The prior art teaches direct solvent extraction which leaves much to be desired in that excessively large quantity of fines are obtained. These tend to clog extraction equipment thereby making it impractical to use this means of extraction commercially.
The literature discloses a commercial production of peanut flour which utilizes a combined prepress solvent extraction method. In that method the peanuts are cooked and screw-pressed at high temperature to obtain a residual oil of about 11% prior to solvent extraction, and that method yields a flour with a tan color and a protein solubility of only 59%, thereby limiting its use in food products. (See "Processing of Edible Flour and Grits," by J. L. Ayres, et al., J. Am. Oil Chem. Soc., 51, 4, 133-136, 1974.)
J. Pominski, et al disclosed the mild cooking/wet heat conditioning of peanuts prior to extraction in "Filtration-Extraction of Peanuts on a Bench Scale," JAOCA 32 (6) (1955). However, no process for obtaining a white, bland food-grade flour is disclosed.
In the above operations peanuts are generally not blanched, i.e., the skins are not removed. When the skins are removed, the following conventional procedure is used: The peanuts are heated to about 180.degree. F. (82.2.degree. C.) for about 20 minutes, which coincidentally reduces the moisture content from about 8% to 5%. Peanuts are then passed through blanching rollers to remove the loosened skins by aspiration. Peanuts with skins removed (blanched) in this manner are then flaked and solvent extracted yield a raw-tasting peanut flour.
Another disadvantage of the processing by the teachings of the prior art, in preparation of the peanuts for extraction, the peanuts are first comminuted (cracked) to a particle size of about 1/8 inch, then "rolled" (flaked through smooth rolls), a procedure that is not conducive to practical oil extraction by the "direct solvent extraction" method because of its tendency to produce troublesome fines. Direct solvent extraction is a method wherein peanuts are not "cooked" and prepressed prior to solvent extraction.
It has been possible to extract the oil from cottenseed and soybean directly with solvent, that is, without first cooking and pressing, but the application of this method to peanuts has not proven feasible. The reason for this is that when the current direct solvent extraction method is applied to peanuts the bed of flakes tend to pack, causing the solvent to channel unevenly through the flakes, resulting in non-homogeneous, high lipids flour or meal. Also, excess fines are produced as the oil is removed, and the fines that are formed tend to block the screens under the bed of flakes, making extraction even more impractical. Fines also get into the oil recovery system and tend to clog equipment such as the solvent evaporators. For these reasons, direct solvent extraction has not been used commercially for peanuts.
Other attempts to achieve similar goals to those of the present invention are indicated in U.S. Pat. No. 3,947,599 wherein peanuts with high oil content are mixed with water to make a slurry from which the volatile flavors are removed; and in U.S. Pat. No. 3,928,635 wherein peanuts are sliced in an effort to prepare peanut flakes for extraction.
U.S. Pat. No. 4,008,210 teaches that in order to obtain high quality, high protein flour from peanuts by direct extraction, the process must include the essential steps of wet heat conditioning followed by flaking and dry heat conditioning.